Maybe this was already brought up, but I didn't see it.
How about your injector? I see you injected the brine into the meat, but were all pieces of the injector sanitized? Maybe a reach but if you nave the same meat injector I have, there are very hard to reach areas in one of the "needles", that could promote bacteria, if not scrubbed, and maybe boiled. I had to buy a brush special for cleaning it
I would think if the meat was turning when you started you would have notice the smell then. I know I've had 1 or 2 pieces of meat, that I tossed, even though the "date" was good, just because I didn't trust the smell, and I would rather lose the money, than make anyone sick.